The present invention relates to a magnetic disk apparatus that can be thinner than conventional ones, and in particular, relates to a magnetic disk apparatus having a magnetic head that is insulated from a metal head carriage.
Magnetic disk apparatus use a magnetic head to perform magnetic recording and reproduction on and from a magnetic disk, while a magnetic head carriage that supports the magnetic head is moved in the direction of the radius of a magnetic disk. A flexible wiring plate is connected to the magnetic head. Reproduction signals of the magnetic head are supplied to a reproduction circuit and magnetic head recording signals are supplied from a recording circuit via the flexible wiring plate.
However, there are magnetic disk apparatus of a dual head type where magnetic heads are in contact with both sides of a magnetic disk. In this type of apparatus, the magnetic head on a lower side of the magnetic disc is provided on the carriage unit at a bottom side of the magnetic disk and recording and reproduction is performed on the bottom side of a magnetic disk. This carriage unit moves along a guide shaft in the direction of the radius of the magnetic disk. The magnetic head on an upper side of the magnetic disk is supported by an arm and performs recording and reproduction on the upper side of the magnetic disk. This arm is mounted on the carriage unit so as to be rotationally movable.
The magnetic head is placed on a metal gimbal plate i.e. a plate spring, so as to be in stable contact with the surface of the magnetic disk. In a conventional apparatus, the magnetic head is supported on the carriage via the gimbal plate. Because of this, the carriage unit is formed of an insulating synthetic resin so that the noise from the side of a base of the apparatus has no influence on the magnetic head.
However, with the recent need to manufacture thinner magnetic disk apparatus, research is also being performed into the manufacture of thinner carriages. However, mechanical strength decreases if the carriage is simply made thinner. In order to prevent this lowering of the mechanical strength, one solution is to manufacture a thin carriage unit from aluminum or some other metal.
When the carriage unit is made of metal and a gimbal plate is directly placed on the carriage unit, the potential of the magnetic head that is supported on this gimbal plate becomes the same potential as a base of the apparatus via the gimbal plate, the metal carriage unit, and a lead screw and other parts. Therefore, it is easy for the magnetic head to be influenced by noise from the side of the apparatus that passes through the base of the apparatus.
Because of this, a plate shaped insulating member is placed on the carriage that is conventionally made of metal, and the gimbal plate is provided on top of this insulating member. In this manner, the insulating member is provided between the gimbal plate and the metal carriage unit and the configuration is such that there is insulation between the metal carriage unit and the magnetic head that is mounted on the gimbal plate. By this means, it is possible to prevent the magnetic head from being influenced by noise from the base of the apparatus that passes through the metal carriage.
Alternatively, a distal end portion of the metal carriage unit can be covered with an insulated synthetic resin. Then, the provision of a metal gimbal plate on the distal end portion of the carriage unit made of synthetic resin insulates the magnetic head on the gimbal plate from the metal portions of the carriage unit.
However, the provision of an insulating member between the metal carriage unit and the gimbal plate increases the number of parts and also increases the amount of time required for assembly. Also, forming the synthetic resin on the distal end portion of the metal carriage unit not only increases the number of parts, but also results in the need for an additional process for forming the synthetic resin on the distal end portion. Because of this, there is the problem that an increased amount of time is needed for manufacturing and manufacturing costs are increased.